How to apply a material to a noise zone?
Here are two ways of doing this, both are using Color Ramp with Constant value, and both can be changed to something else and with white value (from Color Ramp) you can control how much colour will affect area.

Mask between two shaders:

This is best option if you want to have not only different colours, but also different shaders assigned to "frosted" area. 



Different colours for one shader:

This is best suited if you want only to change colours.